This invention relates to packet communications devices and methods and, more particularly, to packet switching devices and methods.
Increasing demand for communications services have generally increased bandwidth requirements for network components. For example, the increased volume of wireless communications has been generally accompanied by an increase in the bandwidth requirements between wireless terminals and base stations. Users demanding more information and more services from their cell phones and other wireless devices can overwhelm available bandwidth. Wireless service providers are migrating to 2.5G and 3G technologies to mitigate this problem. These technologies generally enable more data per broadcast band than 2G technologies, which can be used to give more bandwidth to individual users or to serve more users in the same cell area.
An important aspect of 3G wireless communications systems is closed loop power control. For example, in wideband code division multiple access (WCDMA) systems, it is typically desirable that a base station be capable of telling a mobile terminal to adjust its transmission power within 5 milliseconds after receiving a packet from the terminal. This can be the most constraining limitation on total delay in the base station, as it includes the round-trip delay of received radio signal sample going from an RF card, to a baseband card, and on to a control card, and back to the baseband card, RF card, and antenna. Each base station may have several RF and baseband cards, and signal samples may be transferred between any given RF card and any given baseband card. Reducing latency in transferring data between these cards tends to be important.
Different architectures may be used to convey data between such cards. In a full-mesh architecture, each RF card is connected to each baseband card. A switched architecture provides a multiple-input multiple-output switch between the RF and baseband cards. The switched architecture can provide improved scalability and flexibility, but may add more latency than the full-mesh solution. Also, for smaller systems, a full-mesh architecture may be less expensive than a switched architecture.
Integrated circuits (ICs) have been developed that can support communications between base station components, such as RF cards and baseband cards. For example, Spectrum Signal Processing Inc. offers the ASIC-based Solano™ chip that can be used to interface processors, such as digital signal processors (DSPs), RISC processors, and FPGAs, and sources of data, such as RF cards. The chip includes eight high-speed FIFOs, with associated control logic, that are paired to form four full-duplex channels. Tundra Semiconductor Corporation offers Serial RapidIO® chips that include a switching fabric that can be used to provide a switched architecture between RF and baseband cards.